Ambrose - I love this deeply. But Antoine and Ambrose.. distinct enough?Blaise - The perfect balance of ancient and modern, fiery, great namesake.. Yes.
Cadfael - I never read the books and can’t divorce Cadfael from the PBS “Mystery” character. I hear "cad-file." “Oh Stefan? What a jerk. Into the cad-file he goes.”Cassian - Gentle, saintly, cinnamonish. Cyprian - This one’s a winner. Makes me think of cypress trees, clear blue water, ancient ruins, Othello... And Cy is the best nickname ever!! Cy Twombly is a bonus namesake.Edmund - Stately and teddybearish at once, but tainted by CS Lewis.Elias - Scholarly yes... though it feels a little whispy to me. Still, I like it a lot. Just saw some art by this Nigerian sculptor named El Anatsui. Really incredible stuff and it made me think El would be a good nickname for a boy. Elgin is nice too. I think of the Elgin Marbles, though it’s a Gaelic name.Evander - Handsome, knightly, and I like that it nearly contains “wander.” Maybe not as dimensional as some of your others.Gerard - A nice match for Antoine. Makes me think of the great painter Gerhard Richter. I slightly prefer Jerome (or Geronimo for that matter!)Julian - A beautiful, humble, organic name, and saintly. I know you dislike nicknames, but Jules is fabulous.Laurence - Yes. Remember “Laurence Ranulf Wythe?” That was an incredible concoction Blade. I still mutter it to myself sometimes. Isn’t it a shame LaurenceOlivier is taken? Could a more beautiful name exist?Leander - I love its slinky sound, but sorry.. I find it sort of LittleLord Fauntleroyish. Maybe it just needs the right boxer namesake to butch it up (a la Evander Holyfield.)Lionel - Crazy about this. Bookish yet playful.Lucian - This one’s going stale for me, though it’s a nicely open and elemental name.Malcolm - Cool. Good namesakes, and the sound has a beautiful muffled strength.Marius - I like it, but it is rawther romantic. I imagine a Marius would be versed in celestial navigation, carry a pocketwatch and wear fingerless gloves..Peregrine - Too lacy next to sleek Antoine imo.Sergius - I’m used to Sergei, which is the name of a very greasy man I know. This just doesn’t do it for me. Bodice-ripperish to my ears.Stavros - Intense. My taste-buds aren’t used to it, but I like it. I feel like a Stavros would have long dark eyelashes and tattoos.Victor - Triumphant, uplifting, and adorably old-mannish. Antoine and Victor would be fantastic brother names.

Athanasius - Deliciously obscure yet graceful. A bit lispy.
Auxentius - This just slays me. Glorious. But not worth naming your son George over it. George? I might cry.Esmond - Yes please. This one’s cool like Antoine is cool.
Gratian- I did see “gratin” at first. It’s not as hefty as most of your others, but it’s got a nice meaning and a sweet sound.Ignatius - Very Catholic. I do like its clunkiness. I like that it’s sort of close to “igneous.” I would be compelled to call an Ignatius “Iggy” or maybe Natty.. Bodacious Ignatius... It begs a nickname.Rainier - Yes. Perfect for a misty west coast boy.Sylvan - Prefer Silvius or Silvio, Sylvia or Sylvaine for a girl.
Theodosius - Love it. I’d expect him to be born with a full beard and tortoiseshell glasses. I like that it could be a surfer-dude name too.

Congratulations!
I love Blaise as a brother for Antoine, amazing match. Agree with pps that Leander would be lovely too. Lionel, Gerard, Lucian and Victor would be great choices, as well. I also love Edmund, Peregrine and Ambrose, but I'm not sure they fit with Antoine brilliantly. Can't beat the suggestions offered by others, but I think you already have some really nice options. Looking forward to hearing more about your choices, good luck!

I think I said Congrats before but I'm so excited for a 2nd LittleBlade to be running around.
* Have Combos

Ambrose - I like this name I just don't love it wit Antoine. Your kids deserve distinctly different names for you to "yell" through the house and I think Ambrose and Antoine just don't have that distinction. Blaise - I keep thinking BlaiseBlade. lol. I think my judgement of this name is now tainted as it either being perfect or just weird. But I'm not sure it has the same charm and feathery weight to it that Antoine does.Cadfael - The ending for this is too close to Raphael for me. I don't know why this bothers me as the name itself is fantastic but it does bother me.
*Cassian - Beautiful, soft and handsome. CassianBasil, CassianEdmund, CassianMichael.Cyprian - I love this but (at least when I prn it) the ending is too close to Antoine for me, it doesn't rhyme but is almost sounds like it could. (Does that make sense?)
*Edmund - I adore this name. Edmund Auxentius, EdmundIgnatius.
*Elias - Elias is great. I haven't decided yet if it's the best of your list but I do really like it. EliasDionysius, Elias Orentius.Elgin - it's nice I don't know how it meshes well with Antoine - I feel like you have better options on your list.Evander - Like, just don't love with Antoine.Gerard - I always think or Gerard Depardieu (pronounced zhay-RAHR) when I hear this which makes it awesome in my mind - masculine and soft. However, the English pronunciations (jə-RAHRD, JER-ərd) sound harsh to me and it looses it's charm for me.
*Julian - One of my all time favorites. Julian Theodosius, JulianRainier.
*Laurence - According to behindthename in french this is a womens name and spelling. How about Laurenz or Laurent instead? I don't usually love this name but I think it would be great for Family Blade. Awesome saint name and it has that classy, soft, handsome and masculine feel that are such great components of Antoine. LaurentAmbrose, Laurenz Vitalian.Leander - Great name, I usually love it but somehow just not today.
*Lionel - Awesome choice!! LionelEsmond, Lionel Malchus.
*Lucian - Really love this name. Lucian Emilius, Lucian Pardus.Malcolm - Like the name, don't love it for you.Marius - I keep picturing soccer prodigies when I hear this name. I don't really know why. Peregrine - Too wimpy next to Antoine which has a silent and strong quality to it in comparison to the soft and feminine feel of Peregrine.Sergius - This feels a bit too Alpha-male, I beat my chest with my fists next to Antoine. Stavros - see Sergius.
*Victor - Obviously I love this name - but I am drawn to it for it's strong warrior essence. but I think that maybe you'd be better served with the slightly softer Vincent (also SaintVincent of Lérins). Antoine and Vincent would be awesome. Victor Leontius, VincentIgnatius, Vincent Auxentius.

Athanasius - This feels a bit lispy especially if you choose a "softer" boys name as a FN. Auxentius - Loved it the moment I laid my eyes on it. Esmond - Very handsome and I think this is a wonderful, and intriguing, alternative to Edmund. Gratian - I saw “gratin” at first. I think that would always bother my dyslexic brain. Sylvan - very cool. Theodosius - a bit of a mouthful. I think it could be a wonderful second for a very straight forward first name but if you choose something a bit fancier (and I don't even mean very fancy) it could just be too much.